1. Field of the Invention
This invention relates to a D/A converter for use in various electronic devices, more particularly to a D/A converter suitable for use in an integrated circuit.
2. Description of the Related Art
FIG. 5 shows a conventional resistance-type potential dividing D/A converter. Terminal 51 is supplied with reference voltage Vref, and terminal 52 is grounded. Resistors R2.sup.0 -R2.sup.k having the same resistance are connected in series between terminals 51 and 52. One ends of switches SW2.sup.0 -SW2.sup.k for deriving divided voltages are connected between each adjacent pair of resistors R2.sup.0 -R2.sup.k and to terminal 52. The other ends of switches SW2.sup.0 -SW2.sup.k are connected to output terminal 54 via impedance converter 53.
Input terminal 55 is supplied with digital signal Ds, and connected to decoder 56. Decoder 56 comprises logical circuits L2.sup.0 -L2.sup.k, each of which is constituted by a NAND circuit and the like, and which are connected to the switches SW2.sup.0 -SW2.sup.k, respectively. The digital signal supplied to input terminal 55 is decoded by these logical circuits L2.sup.0 -L2.sup.k, the decoded outputs switch the corresponding switches SW2.sup.0 -SW2.sup.k, and an analog voltage corresponding to the input digital signal is output from output terminal 54.
The above conventional D/A converter needs to have more resistors to process input data formed of more bits. The more resistors, the more switches and logical circuits are required. Since a logical circuit constituting a decoder has a lot of elements, an increase in the number of logical circuits results in a great increase of the size of the D/A converter. Hence, when a D/A converter is incorporated in an LSI using MOS transistor, it occupies a large area on the LSI chip, resulting in a high manufacturing cost.